Method and apparatus for simultaneously retrieving portions of a data stream from different channels

ABSTRACT

An apparatus and method for simultaneously processing each of a plurality of carrier signals having data modulated thereon, wherein a complete data stream is formed by extracting at least portions of at least two of the modulated signals and combining the extracted portions. Each of the portions of the complete data stream comprises a plurality of packets having associated with them respective stream identification and sequence codes, where the stream identification identifies the complete bit stream to be formed, and the sequence codes identify the order or position within the complete bitstream that the associated data packets should be inserted.

[0001] This application is related to simultaneously filed U.S. patentapplication Ser. No. ______, filed ______ (Attorney Docket No. PU010164)entitled, METHOD, APPARATUS AND DATA STRUCTURE ENABLING MULTIPLE CHANNELDATA STREAM TRANSMISSION, which is incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

[0002] The invention relates to communications systems and, moreparticularly, a receiver capable of simultaneously receiving from eachof a plurality of data channels respective portions of a data stream.

[0003] Communications systems having higher data throughput and greaterefficiency in the use of available bandwidth are increasingly in demand.In a typical communications system, such as a satellite communicationssystem, a satellite provides a plurality of communications channels toterrestrial receivers. Each communications channel has associated withit, for example, a particular transponder, a particular polarization andthe like. Normally, each defined channel broadcasts at its maximum datarate.

[0004] Where the amount of data to be transmitted is less than theamount of data that a channel is capable of transmitting, the definedchannel is underutilized. In this case, the defined channel may transmitNULL packets during those time slices within which there is no dataavailable to be transmitted. Where the data to be transmitted requiresmore bandwidth than is available on the channel, an alternate channelhaving greater available capacity must be selected. Thus, communicationschannels typically operate at less than a 100% utilization level due tothe likelihood that the number of data streams to be transmitted, andthe amount of data within each stream, are likely not to match thebandwidth available in the transmission channels.

SUMMARY OF THE INVENTION

[0005] The invention comprises an apparatus and method forsimultaneously processing each of a plurality of carrier signals havingdata modulated thereon, wherein a complete data stream is formed byextracting at least portions of at least two of the modulated signalsand combining the extracted portions. Each of the portions of thecomplete data stream comprises a plurality of packets having associatedwith them respective stream identification and sequence codes, where thestream identification identifies the complete bit stream to be formed,and the sequence codes identify the order or position within thecomplete bitstream that the associated data packets should be inserted.

[0006] An apparatus, in accordance with an embodiment of the presentinvention, comprises an analog to digital converter, for directlyconverting a plurality of carrier signals into a digital data stream; aplurality of channel processors, for simultaneously extracting from thedigital data stream data carried by respective carrier signals; and aprocessor, for combining at least portions of the data extracted from atleast two carrier signals to produce a complete bitstream, the extracteddata having associated with it stream identifier and sequence codeinformation for determining, respectively, the complete bitstreamcorresponding to the extracted data and the sequence within the completebitstream of the extracted data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The teachings of the present invention can be readily understoodby considering the following detailed description in conjunction withthe accompanying drawings, in which:

[0008]FIG. 1 depicts a high-level block diagram of an exemplary receiverusable in accordance with the principles of the invention;

[0009]FIG. 2 depicts a graphical representation of a DBS frequency plan,exemplary of a frequency plan which may be used in accordance with theprinciples of the invention;

[0010]FIG. 3 depicts an exemplary data structure used in accordance withthe principles of the present invention;

[0011]FIG. 4 depicts a exemplary high-level block diagram of a back-endprocessor suitable for use in the receiver of FIG. 1, and in accordancewith the principles of the present invention;

[0012]FIG. 5 depicts a exemplary flow diagram of a method in accordancewith the principles of the present invention; and

[0013]FIG. 6 depicts a exemplary graphical representation of packetstream processing in accordance with the principles of the presentinvention.

[0014] To facilitate understanding, identical reference numerals havebeen used, where possible, to designate identical elements that arecommon to the figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015]FIG. 1 depicts a high-level block diagram of an exemplary receiverusable in accordance with the principles of the invention. Specifically,the receiver 100 comprises a direct broadcast satellite (DBS) receivercomprising an analog processing section 110, an analog-to-digital (A/D)converter 120, a plurality of channel processors 130 ₁ through 130 _(n)(collectively channel processors 130), a back end processor 140 and,optionally, a mass storage device 150.

[0016] The analog processor 110 receives an analog input signal S1comprising, illustratively, a 950-1,450 MHz signal having modulatedthereon a plurality of analog carrier signals having, illustratively,bandwidths of 24 MHz and center frequencies separated by 29.16 MHz fromthe center frequencies of adjacent analog carrier signals. The analogprocessor 110 performs a signal conditioning function to produce anoutput signal S2 suitable for processing by the A/D converter 120.

[0017] The analog processing section 110 comprises the seriescombination of an optional first analog gain control (AGC) functionblock 112, a bandpass filter 114, an amplifier 116 and a second AGC 118.The first optional AGC amplifies the input signal S1 (as needed). Thebandpass filter 114 rejects out-of-band frequency components (e.g.,those frequency components approximately below 950 MHz and above 1,450MHz). The amplifier 116 boosts the resulting passband limited signal toa level appropriate for processing by the A/D converter 120. The AGC 118operates to insure that the amplified signal remains consistent over arelatively large range of input signals, such as is available from the“outdoor” portion (i.e., satellite disk and associated circuitry) of asatellite system. The output signal S2 comprises, illustratively, theinput signal S1 having been processed to provide 50 db gain and 45 dbautomatic gain control.

[0018] The A/D converter 120 receives all (illustratively) 16 channelssimultaneously and produces at its output a digital bit stream S3 thatis representative of the 16 channels in a digital format. In theexemplary satellite receiver embodiment, the A/D converter 120 comprisesan 8 bit A/D converter approximately 1.5 GHz. Thus, given the relevantinput frequencies of signal S2 of 950 to 1,450 MHz, the output signal S3comprises a digital signal having an inverted spectrum from 50 to 550MHz. The output signal S3 of the A/D converter 120 is coupled to aninput of each mixer 132 within the channel processors 130 ₁ through 130_(N).

[0019] The A/D converter 120 comprises a high-speed analog-to-digitalconverter operating at a sampling rate of FS. The A/D converter 120receives the signal S2 including, illustratively, the frequencycomponents associated with each of 16 transponders having the samepolarization (i.e., left hand or right hand) within a DBS system. Withinthe context of a DBS system such as directTV, left hand and right handcircular polarization is utilized in a known manner to increase theavailable bandwidth and, therefore, increase the total number ofchannels that may be provided to customers.

[0020] In one embodiment of the invention, the A/D converter 120operates with a sampling frequency below 950 MHz. In another embodimentof the invention, the A/D converter 120 does not use undersampling.Specifically, in this embodiment of the invention, the Nyquist criteriais satisfied by sampling at two times the highest frequency (i.e., 3GHz). However, since the bandpass filter 114 and the analog processor110 band limit the input signal, such a high sampling rate may beavoided using the undersampling techniques described herein. Byutilizing a lower sampling frequency, a lower cost A/D converter may beemployed.

[0021] Each of the channel processors 130 comprises a mixer 132, adecimator/filter 134, a digital demodulator 136 and a transportprocessor 138. It will be appreciated by those skilled in the art thatthe digital demodulator 136 and transport processor 138 may be combinedinto a single integrated circuit known as a link IC.

[0022] Each of the mixers 132 mixes the digital signal S3 with arespective numerically controlled oscillator (NCO) signal to producerespective in-phase I and quadrature Q signal components, which arecoupled to the respective decimator/filters 134. The respective NCOfrequency is selected to derotate a desired signal or channel. Eachmixer 132 operates to perform a frequency rotation function, whereby theselected channel is rotated to baseband from the undersampled digitalsignal S3. This may be accomplished using a numerical table to extract(or rotate) the desired channel frequency from the digital signalcomprising all available frequencies processed by the A/D converter 120.

[0023] The decimator/filter 134 receives the respective in-phase I andquadrature Q components of the derotated and selected channel. Thedecimator/filter 134 processes these orthogonal components to extractthe desired signal. Briefly, after the mixer 132 derotates the selectedsignal to baseband (i.e., by multiplying the signal by sine and cosinefunctions), non-desired channel energy is removed from the derotatedsignal. Specifically, given the exemplary embodiment whereby 16 channelsare simultaneously processed, it is desired to retain only the channelenergy associated with a specific desired channel. After filtering thederotated baseband signal to remove undesired channel energy, theremaining signal is decimated to remove excess energy associated withthe desired channel. For example, since the sampling frequency of theA/D converter is 1.5 gigasamples per second, frequency components fromzero to 750 MHz may be present. Those samples not associated with the(approximately) 24 MHz associated with a selected channel areunnecessary. The decimation process removes the unwanted samples. Aswill be appreciated by those skilled in the art, the 24 MHz associatedwith a selected channel is actually two 12 MHz channels due to thesine/cosine processing of the derotator or mixer 132. The resultingderotated, filtered, and decimated signal is then provided to therespective demodulator 136.

[0024] The demodulator 136 operates to demodulate the provided signaland retrieve therefrom the original data stream modulated thereon. Sinceeach of the channel processors 130 operates simultaneously, therespective demodulators 136 are operating upon substantiallysimultaneous transmitted streams. The digital demodulators 136 providerespective demodulated data streams to the respective transportprocessors 138.

[0025] In an exemplary embodiment, the A/D converter 120 operates usingan 8 bit sample. Within a DBS system, a 4-bit sample is typicallyutilized for QPSK demodulator. More or fewer bits may be used for othermodulation schemes. However, since the A/D converter 120 in theexemplary embodiment operates to undersample a bandwidth-limited DBSsignal comprising 16 channels, and since the amount of resolutionrequired is a sum of powers relationship, one channel normallydemodulated is decoded with 4-6 bits of resolution scales toapproximately 16 channels being demodulated or decoded using 8 bits ofresolution. Those skilled in the art will know that more or fewer bitsof resolution may be employed where the accuracy of the A/D converter120 is increased or decreased, the initial coding scheme utilizes a morecomplex topology and other factors.

[0026] In one embodiment of the invention, the transport processors 138provide baseband video and audio streams to the back-end processor 140.In this embodiment of the invention, the various transport processors138 ₁ through 138 _(N) communicate with each other and otherwiseexchange information such that the baseband audiovisual streams may berecreated by extracting stream portions from the various channels andassembling the extracted stream portions into an entire audiovisualstream or streams. In an alternate embodiment of the invention, eachtransport processor 138 provides one of an output transport stream orseveral elementary streams which are subsequently combined into a singletransport stream including audiovisual sub-streams, or the audiovisualsub-stream portions are combined into complete audiovisual sub-streams.

[0027] In the embodiment whereby the transport processors 138 providebaseband video and/or audio information, such baseband video and/oraudio information is provided to baseband audiovisual processors forstandard processing prior to presentation. In the case of the output ofthe transport processors 138 comprising encoded audiovisual information,such encoded audiovisual information is provided to appropriate audioand video decoders for processing prior to presentation.

[0028] The optional mass storage device 150 may be used to storeportions of a complete bitstream that are transported via a plurality ofchannels and received over a relatively long period of time. Forexample, a server may transmit to the receiver a movie or other contentvia a plurality of channels in non-real-time, such as overnight. Thus,in this embodiment of the invention, the mass storage device 150 is usedto store a file piece by piece in response to the reception andprocessing of pieces or portions of the file by the various channelprocessors 130.

[0029] A network packet structure suitable for implementing the presentinvention will be described in more detail below with respect to FIG. 3.Briefly, the network packet structure 300 of FIG. 3 provides for theinclusion within a payload portion of one or more packets from theinitial packet stream. Additionally, within the network packet payloadportion or header portion is included information suitable for reformingthe sequence of the initial packet stream. Additionally, identificationinformation is provided such that a plurality of initial packet streamsmay be reformed at one or more receivers.

[0030] In addition to the regular overhead that is carried by the choiceof encoding and/or modulation within the communications system, thefollowing information may also be included: (1) the number oftransponders employed within the communications system and theidentification of those transponders used to carry desired data; (2) thetiming of the use of the employed transponders, including informationrelevant to changing between different transponders for contiguous dataor related data streams; (3) the order of the data transmitted and anyredundancy of such data, along with a map or other means forfacilitating the recombination of such data; and (4) default displayinformation.

[0031]FIG. 2 depicts a graphical representation of a DBS frequency plan,exemplary of a frequency plan which may be used in accordance with theprinciples of the invention. Specifically, FIG. 2A depicts the nominalDSS frequency plan for right hand circularly polarized (RHCP) channels,while FIG. 2B depicts the nominal DSS frequency plan for left handcircularly polarized (LHCP) channels. Given a total of, illustratively,32 channels, the 16 odd channels are RHCP channels and are shown in FIG.2A, while the 16 even channels are LHCP channels and are shown in FIG.2B. The odd channels start at a channel center frequency of 974.0 MHz(channel 1) and extend to 1,413.4 MHz (channel 31). Each channel is 24MHz in width, each center frequency is separated by an adjacent centerfrequency by 29.16 MHz. Similarly, the even channels start at a channelcenter frequency of 988.5 MHz (channel 2) and extend to a channel centerfrequency of 1,425.98 MHz (channel 32). DSS is a trademark of HughesElectronics. A packet structure suitable for use within the DSS systemis described in “DSS Transport Protocol” Version 1.1, Feb. 12, 1996,which protocol is incorporated herein by reference in its entirety.

[0032] In one embodiment of the invention, the 32 channels provided bythe network interface/link 130 of FIG. 1 substantially conform to theDSS frequency plan of FIG. 2. However, it will be appreciated by thoseskilled in the art that the present invention may be practiced with anyfrequency plan and any number of channels. It is noted that the subjectinvention finds particular utility within the context of two or moretransmission channels due to the ability to split or distribute aninitial packet stream among the two or more transmission channels.

[0033]FIG. 3 depicts an exemplary data structure used in accordance withthe principles of the present invention. Specifically, the datastructure 300 comprises a packet structure having a header portion 310and a payload portion 320.

[0034] The header portion 310 comprises standard header data 311, streamidentifier data 312, and sequence code 314. In one embodiment, theheader portion 310 is further augmented by other data 316.

[0035] The payload portion 320 is used to carry one or more packetsfrom, for example, an initial packet stream. By associating each of theone or more initial packets of the payload portion with a streamidentifier and sequence code, a receiver may rearrange packets receivedfrom a plurality of transport channels to produce the initial packetstream for subsequent processing. In this manner, an initial packetstream may be transported using a plurality of transport channels andreformed at a receiver for subsequent processing. In the case of aplurality of packets being included within a payload portion of anetwork packet data structure, the plurality of packets or a group ofpackets are preferably arranged in a known sequence such that a singlesequence code may represent the point within an initial bit stream thatthe entire group of packets should be inserted.

[0036] In one embodiment, one or more initial data stream packets suchas Moving Picture Experts Group (MPEG) transport packets are carriedwithin the payload data portion 320 of an internet protocol (IP) packet300. The standard header data 311 of the header portion 310 is augmentedby including a stream identifier 312 and sequence code 314 indicativeof, respectively, the specific initial data stream to which the one ormore packets within the payload belong, and the sequence within thatspecific initial data stream of the one or more packets within thepayload portion. It is assumed that the one or more MPEG transportpackets within the payload portion of the carrier packet structure arearranged in the same order in which they are normally provided in theMPEG transport stream itself, although schemes not so arranged may alsobe implemented and still incorporate and embody the principles of thepresent invention.

[0037] In a “channel hopping” embodiment of the invention, the streamidentifier data 312 and sequence code 314 associated with one or morepackets or groups of packets within a payload portion of the datastructure 300 of FIG. 3 are augmented by other data 316 comprising achannel identifier field and a time of transmission field. The channelidentifier data is used to identify which transmission or transportchannel(s) will be used to transport the stream identified in field 312.The time of transmission data is used to indicate the actual time ofsuch transmission(s). In this manner, where a receiver is capable ofprocessing a smaller number of transport channels, a “channel hopping”mechanism is implemented whereby one or more of the channel processorsat the receiver select the identified channel(s) at the identifiedtime(s) to retrieve therefrom the stream identified in field 312.

[0038] To reduce the number of channel processors, in one embodiment ofthe invention, only a subset of the received channels is processed. Inthis embodiment, a transmitter inserts content into several transportchannels for subsequent processing by a receiver. Similarly, thereceiver processes each of the transport channels to retrieve theinserted content. For example, in one embodiment a receiver provides,illustratively, two channel processors 130, each of which is capable ofprocessing any one of, illustratively, 16 received transport channels.In this embodiment, in addition to stream identification and sequencecode information, channel information and transmit timing information isalso provided to enable the “channel hopping” scheme. In this channelhopping scheme, transported data associated with a single identifiedstream is provided via a plurality of transport channels. The channelinformation and time information indicate, respectively, which channelis providing the data and at what time is that channel providing thedata.

[0039] In this manner, one or more channel processors may be caused toprocess different channels at different times to selectively retrievepackets associated with a desired identified data stream. Thisembodiment of the invention is especially useful where some of thechannels are not available at some times. Thus, when allocating data tobe transmitted among the available transmission channels, the actualchannel and time of allocation is predetermined, and this predeterminedtime and channel allocation is inserted into the data stream to betransmitted to the receiver. The receiver must receive this informationwith sufficient time to adapt a particular channel processor to retrievethe desired data at the appropriate time.

[0040]FIG. 4 depicts a exemplary high-level block diagram of a back-endprocessor suitable for use in the receiver of FIG. 1, and in accordancewith the principles of the present invention. The back-end processor 140of FIG. 4 receives a plurality of transport stream portions T₁ throughT_(N) from the channel processors 130 ₁ through 130 _(N). The back-endprocessor 140 recombines appropriate transport stream portions (orelementary stream portions) to produce one or more transport streams.The one or more transport streams are further processed to extractelementary streams included therein, such as video streams, audiostreams, data streams and other streams (or elementary streams). Theelementary streams are then coupled to appropriate processing elements,such as decoders, data processors and the like. Thus, the back-endprocessor 140 receives a plurality of transport stream portions T1through TN and responsively produces one or more retrieved data streamstherefrom.

[0041] The back-end processor 140 comprises a processor 144 as well asmemory 146 for storing various programs 146P. The processor 144cooperates with conventional support circuitry 148, such as powersupplies, clock circuits, cache memory and the like as well as circuitsthat assist in executing the software routines stored in the memory 146.As such, it is contemplated that some of the process steps discussedherein as software processes may be implemented within hardware, forexample, as circuitry that cooperates with the processor 144 to performvarious steps. The processor 144 also contains input/output (I/O)circuitry 142 that forms an interface between the back-end processor140, the channel processors 130 and any elementary stream processingdevices (not shown). Although the back-end processor 140 of FIG. 4 isdepicted as a general-purpose computer that is programmed to performvarious detection and processing functions in accordance with thepresent invention, the invention can be implemented in hardware as, forexample, an application specific integrated circuit (ASIC). As such, theprocess steps described herein are intended to be broadly interpreted asbeing equivalently performed by software, hardware, or a combinationthereof.

[0042]FIG. 5 depicts a exemplary flow diagram of a method in accordancewith the principles of the present invention. Specifically, FIG. 5depicts a flow diagram of a method 500 implementing various functions ofthe receiver 100 of FIG. 1. It is noted that the functions of the analogprocessor 110 are shown as steps 505-510; the functions of the A/Dconverter 120 are shown as step 515; the functions of channel processors130 are shown as steps 525-540; and the functions of the back-endprocessor 140 are shown as step 545.

[0043] At step 505, a block of carrier frequencies including transportor carrier channels of interest are received. At step 510, the receivedchannel block is band limited to exclude frequencies outside the blockof desired channels. At step 515, the band-limited block of frequenciesis digitized using, preferably, an undersampling technique. Thedigitizing function is described in more detail above with respect toA/D converter 120 of FIG. 1. The reception and band limiting functions505, 510 are described in more detail above with respect to the analogprocessor 110 of FIG. 1.

[0044] At step 520, each of the channels of interest within thedigitized and band-limited block of channels is derotated to produce arespective derotated stream providing the channel of interest. At step525, each of the derotated streams is filtered to remove the channelenergy of other channels (i.e., the channel energy associated withchannels not to be processed by the particular channel processor 130).At step 530, each of the filtered and derotated streams is decimated toremove excess samples. At step 535, each of the decimated streams isdemodulated to recover the respective carrier transport streams. Aspreviously discussed, the carrier transport streams include indicia ofstream identifier and sequence code for each packet or group of packetsused to form, illustratively, an MPEG transport stream. Optionally, thetransport streams include channel identification and time oftransmission data. The functions of steps 520-540 are discussed in moredetail above with respect to the channel processors 130 of the receiver100 of FIG. 1.

[0045] At step 540, the transport stream portions are retrieved from thecarrier transport streams. At step 545, the transport stream portionsare combined into whole transport streams using the stream ID andsequence code information. The combined transport streams are thenprocessed in a standard manner by video decoders, audio decoders, dataprocessors or other elementary stream processing circuitry.

[0046] In one embodiment of the invention, only a subset of the receivedchannels is processed. That is, to reduce costs and complexity withinthe receiver 100 of FIG. 1, two or more channel processors 130 areutilized. However, the number of channel processors 130 actuallyutilized is less than the number of channels present within outputsignal S3 of the A/D converter 120. In this embodiment, channelidentifier and channel transmit time information is utilized to cause atleast one of the channel processors 130 to selectively process differentchannels at different times. In this manner, the selected at least onechannel processor is caused to “hop” between different channels suchthat all of the data necessary to reconstruct an initial bitstream maybe retrieved utilizing less than a full complement of channelprocessors.

[0047]FIG. 6 depicts a graphical representation of exemplary packetstream processing performed in accordance with the principles of thepresent invention. Specifically, a nominal transmission channel packetstream 610 is shown comprising a plurality of data packets D1interspersed with NULL packets N. After processing according to theinvention, the NULL packets N in the nominal transport stream 610 arereplaced by packets from a plurality of inserted streams. Specifically,a modified stream 620 is shown comprising the initial data packets D1interspersed with inserted data packets X1 and X2 from the respectivebitstreams. In this manner, upon transmitting the modified stream 620,no bandwidth is wasted by transmitting NULL packets.

[0048] At a receiver, the main channel data packets D1 are retrieved asdata stream 630, the first inserted stream packets X1 are retrieved asdata stream 640 and the second inserted stream packets X2 are retrievedas data stream 650. It is noted that each of the packets X inserted intothe stream conform to the packet structure discussed above with respectto FIGS. 1 through 5.

[0049] A method, apparatus, and data structure suitable for use in atransmitter within a system, in accordance with the principles of thepresent invention, are disclosed in simultaneously filed U.S. patentapplication Ser. No. ______ (Attorney Docket No. PU010164). In thatdisclosure, apparatus and method are provided wherein a data stream tobe transmitted to a receiver comprising a plurality of data packetstructures is encapsulated within a data packet structure adapted to atransmission medium or network. Each packet or group of packets includedwithin a payload portion of the encapsulating data structure isassociated with a stream identification and sequence code, as discussedabove. In one embodiment, the header portion of the network packetstructure is adapted to include a stream identifier field and a sequencecode field for storing this information. In one embodiment, the headerportion of the network packet structure is further adapted to include achannel identifier field and a time of transmission field foridentifying which transport channel will carry desired data, and at whattime the desired data will be carried. In another embodiment, the fieldsare inserted into the header portions of the underlying packets to betransported (i.e., the packets to be encapsulated). Also disclosed istransmission channel bandwidth monitoring and utilization apparatus andmethods, whereby a single datastream to be transmitted may be conveyedto a receiver using multiple channels by, illustratively inserting datapackets within the data stream in place of NULL packets. The NULLpackets are normally inserted within a data stream channel when data tobe transmitted is not otherwise available. The processing of NULLpackets is discussed in more detail in the above-referenced U.S. patentapplication.

[0050] The receiver of the present invention, by simultaneouslyprocessing multiple received channels and extracting therefromrespective portions of a complete bitstream allows more efficientutilization of the available bandwidth of each channel to be processed.

[0051] Advantageously, a receiver in accordance with the principles ofthe present invention, eliminates the typical analog conversion stagefound in a direct conversion receiver. Specifically, the analog mixersand oscillators are avoided. Previous arrangements directly convert tobaseband a single channel, such as the frequencies associated with onechannel of either right hand or left hand circular polarization asprovided by a single transponder.

[0052] The invention provides the capability to not only down convert orreceive one channel, but to receive N channels simultaneously. All ofthe N down-converted channels are included within a digital bit stream,which is processed digitally to recover in parallel any of the Noriginal transponder channels. In an analog system, such capabilityrequires the use of N analog tuners to select the N analog signals forsubsequent processing. Since the N analog tuners at subsequentprocessing operate on RF signals that cannot be split due to the powerdomain processing of such signals, the N analog tuners would be gangedtogether. Within the context of the present invention, the directconversion processing of multiple channels simultaneously avoids thishigh cost tuning and processing arrangement.

[0053] Although various embodiments, which incorporate the teachings ofthe present invention, have been shown and described in detail herein,those skilled in the art can readily devise many other variedembodiments that still incorporate these teachings.

What is claimed is:
 1. A method, comprising: converting a plurality of carrier signals into a digital data stream; extracting from said digital data stream, data carried by at least two carrier signals; and combining at least portions of data extracted from said at least two carrier signals to form a complete bitstream, said extracted data having associated with it stream identifier and sequence code information for, respectively, identifying the complete bitstream corresponding to the extracted data and determining the position of the extracted data within the complete bitstream.
 2. The method of claim 1, wherein said complete bitstream comprises a transport stream, said method further comprising: selecting those transport packets within the extracted data having a stream identifier corresponding to said complete bitstream; and arranging the selected packets according to the respective sequence codes to form said complete bitstream.
 3. The method of claim 1, wherein the extracted data comprise transport stream packets according to a first transport format, and the complete bitstream comprises a transport stream packet of the first transport format.
 4. The method of claim 1, wherein the extracted data comprise transport stream packets according to a first transport format, and the complete bitstream comprises a transport stream of a second transport format.
 5. The method of claim 4, wherein transport stream packets according to said first transport stream format are carried within a payload portion of transport stream packets according to said second transport format.
 6. The method of claim 5, wherein said stream identifier and said sequence code is stored in a header portion of said transport stream packets according to said first format.
 7. The method of claim 1, wherein said step of directly converting comprises: band limiting a received signal to pass said plurality of carrier signals; and converting the band limited received signal to a digital signal.
 8. The method of claim 1, wherein said step of simultaneously extracting comprises: derotating each of the digitized plurality of carrier signals to produce respective derotated carrier signals; and demodulating each of at least two filtered carrier signals to extract therefrom respective data bearing streams.
 9. The method of claim 8, wherein said step of simultaneously extracting further comprises: filtering each of the derotated carrier signals to reduce non-channel spectral energy; and decimating each of the filtered signals to reduce the number of data-representative samples.
 10. The method of claim 1, wherein some of said extracted data has associated with it channel identification and time of transmission information for, respectively, indicating which of said plurality of carrier signals will carry portions of said complete bitstream and the time said portions will be carried.
 11. The method of claim 1, wherein said step of simultaneously extracting includes: identifying a carrier signal having data corresponding to a desired complete bitstream; and processing said identified carrier signal to extract said data corresponding to said desired complete bitstream.
 12. The method of claim 11, wherein said step of simultaneously extracting further includes: determining when said identified carrier signal will include said data corresponding to said desired complete bitstream, said identified carrier signal being processed at said determined time.
 13. The method of claim 11, wherein some of said extracted data has associated with it channel identification information for indicating which of said plurality of carrier signals will carry said data corresponding to said desired complete bitstream.
 14. The method of claim 13, wherein said extracted data is associated with said channel identification information and also is associated with time of transmission information for indicating the time when said identified carrier signal will include said data corresponding to said desired complete bitstream.
 15. The method of claim 6, wherein some of said transport stream packets according to said first format have stored therein within said header portion channel identification and time of transmission information for, respectively, indicating which of said plurality of carrier signals carry portions of said complete bitstream and the time said portions will be carried.
 16. A method, comprising: band limiting a received signal to pass a plurality of carrier signals, each of said carrier signal having modulated thereon, and within a channel bandwidth, a respective data bearing stream; converting the band limited received signal to a digital signal; derotating each of the digitized carrier signals to produce respective derotated carrier signals; demodulating each of at least two filtered carrier signals to extract therefrom respective data bearing streams; and combining data from at least two data bearing streams into a resultant data stream, said at least two data bearing streams comprising respective portions of said resultant data stream.
 17. The method of claim 16, further comprising: filtering each of the derotated carrier signals to reduce non-channel spectral energy; and decimating each of the filtered signals to reduce the number of samples representing each data bearing stream.
 18. The method of claim 16, wherein said resultant data stream comprises a transport stream, said method further comprising: identifying those transport packets within said first and second data bearing streams being associated with a stream identifier corresponding to said resultant stream; and arranging the identified packets according to a respective sequence codes associated with said identified packets to form said resultant stream.
 19. The method of claim 18, wherein each of said simultaneously demodulated data bearing streams are transport streams according to a first transport format, and said resultant data bearing stream is a transport stream according to a second transport format.
 20. The method of claim 16, wherein the data bearing streams comprise transport streams according to a first transport format, and the resultant data stream comprises a transport stream of said first transport format.
 21. The method of claim 16, wherein the data bearing streams comprise transport streams according to a first transport format, and the resultant data stream comprises a transport stream of a second transport format.
 22. The method of claim 21, wherein data according to said second transport stream format is carried within a payload portion of data packets according to said second format.
 23. The method of claim 22, wherein each of said data packets according to said second format includes, in a header portion, a stream identifier and sequence code for data carried within a respective payload portion.
 24. A method, comprising: band limiting a received signal to pass substantially those frequencies occupying a spectral region between a first frequency f₁ and a second frequency f₂; converting, using an analog-to-digital converter having a sampling rate f_(S), the band-limited signal to produce a digital signal therefrom, said sampling rate f_(S) being greater than f₂; derotating each of a plurality of data bearing signals within said digital signal to produce respective derotated signals; filtering each of the respective derotated signals to remove channel energy outside of the respective defined channel; decimating each of the filtered and derotated signals to reduce the number of samples representing each data bearing signal; demodulating each of at least two filtered carrier signals to extract therefrom respective data bearing signal; and combining at least respective portions of at least two of the resulting decimated data bearing signals into a single data signal.
 25. Apparatus, comprising: an analog to digital converter, for converting a plurality of carrier signals into a digital data stream; a plurality of channel processors, for extracting from said digital data stream, data carried by respective carrier signals; and a processor, for combining at least portions of said data extracted from at least two carrier signals to produce a complete bitstream, said extracted data having associated with it stream identifier and sequence code information for determining, respectively, the complete bitstream corresponding to the data and the sequence within the complete bitstream of the data.
 26. The apparatus of claim 25, wherein each of said channel processors comprises: a derotator, for derotating a respective digitized carrier signal to produce a respective derotated carrier signal; and a demodulator, for demodulating said respective derotated carrier signal to extract therefrom a data stream.
 27. The apparatus of claim 25, wherein each of said channel processors further comprises: a filter, for filtering the respective derotated signals to remove channel energy outside of the respective defined channel; and a decimator, for decimating each of the filtered and derotated signals to reduce the number of samples representing the respective data.
 28. The apparatus of claim 25, further comprising: a band limiter, to primarily pass only the plurality of carrier signals and respective data modulated thereon; wherein said analog to digital converter utilizing a sampling rate less than twice the maximum frequency of interest within the plurality of data channels.
 29. The apparatus of claim 25, wherein plurality of carrier signals substantially conform to a commonly polarized group of channels provided by a transponder. 